Water treating equipment providing coalescence and flotation within a single vessel

ABSTRACT

A vessel for treating an oil-in-water inlet stream houses an inlet flow distributor arranged to direct an inlet flow toward a perforated baffle of a coalescing section, the coalescing section housing a packing and being arranged upstream of a second baffle; a flotation section arranged to receive a flow exiting the coalescing section and being divided by one or more perforated baffles; and an outlet water collecting pipe arranged to receive a flow exiting the flotation section, the outlet water collecting pipe having one or more openings located along its length. The coalescing section may be divided into two sections, with one section preferably housing a different pre-selected sized packing than the other section. The flotation section may include one or more gas-inducing devices. A solid baffle may be arranged downstream of the second baffle and ahead of the flotation section to provide single or dual flow through that section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application which claims priority toU.S. patent application Ser. No. 14/452,935 filed on Aug. 6, 2014, whichis incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to systems and apparatuses designed for watertreatment. More specifically, the invention relates to water treatingequipment in which coalescence and flotation can occur within a singletreatment vessel.

Selection of water treating equipment is typically based on inletconditions, outlet specifications required, and operating conditionssuch as temperature and chemical used for the treatment. Inletconditions include oil droplet size and concentration; inlet fluidphysical and chemical properties such as API gravity of oil and salinityof produced water; and the type of chemical and dosage used for thetreatment.

Outlet specifications required depend on whether onshore or offshoredischarge or reinjection is involved. For offshore discharge, the outletspecification, which can vary by location and country, is typicallyabout 29 ppm of oil-in-water for the Gulf of Mexico. For reinjection,the outlet specification can depend on such factors as the type ofreservoir involved (e.g. a tight formation or not). Typically, theoutlet oil and solid specifications are less than 5 ppm.

For an offshore discharge application to meet the 29 ppm specification,a liquid/liquid hydrocyclone unit followed by a flotation unit is thepreferred process flow scheme. The hydrocyclone unit is typicallycompact to reduce space and weight requirements.

For an onshore discharge or reinjection application to meet the lessthan 5 ppm specification, a skimmer followed by a corrugated plateinterceptor (“CPI”) followed by flotation unit and nutshell filter unitis the preferred process flow scheme. Because the largest CPI can onlyprocess up 60,000 barrels/day of fluid, a large throughput facility(e.g., greater than 240,000 barrels/day) would require at least fourtrains to process that throughput.

SUMMARY OF THE INVENTION

A vessel or cross-flow scrubber made according to this invention, and amethod for its use, can handle a throughput of at least 60,000barrels/day and up to 240,000 barrels/day or more in single vessel andstill meet less than a 5 ppm specification when used in combination witha nutshell filter located downstream, thereby making the system morecompact when compared to the use of corrugated plate inceptors (“CPIs)and reducing construction costs relative to CPI trains. The scrubber'sinlet distributor, coalescing section, flotation section, internalbaffle design, outlet water collection pipe all work in combination toreduce the cost of construction and increase performance by at least 50%for a given level of throughput relative to vessels which contain eithercoalescence or flotation and CPI trains. The flow rate through thevessel can be a range of 1 ft/min to 10 ft/min (0.3048 m/min to 3.048m/min) and is preferably in a range of 2 ft/min to 5 ft/min (0.6096m/min to 1.524 m/min).

In one preferred embodiment, the vessel extends in a longitudinaldirection and houses:

-   -   an inlet flow distributor arranged to direct an inlet flow        toward a perforated baffle located ahead of a coalescing        section, the coalescing section housing a packing and being        arranged upstream of a second perforated baffle which,        optionally, can be followed by a solid baffle;    -   a flotation section arranged to receive a flow exiting the        coalescing section, the flotation section being divided by one        or more perforated baffles and which may include one or more        gas-inducing devices; and    -   an outlet water collecting pipe arranged to receive a flow        exiting the flotation section, the outlet water collecting pipe        having one or more openings located along its length.

The coalescing section may be divided into a first and a second section,with the packing of the first section being a different pre-selectedpacking than the packing of the second section. The packing in eachsection preferably differ according to size but could also differaccording to shape and material. Preferable shapes include coalescingballs and coalescing rings. The coalescing section may also include asolids removal device which creates a cyclonic flow about the solidsremoval device and fluidizes the solids which have settled to the bottomof that section.

The perforated baffle and second perforated baffle located respectivelyahead and behind the coalescing section distribute flow uniformly across(or through) the vessel. The optional solid baffle can be arranged toprovide single direction flow or dual direction flow through theflotation section. Perforated baffles in the flotation section dividethe section into cells and distribute flow uniformly across or throughthat section.

The inlet flow distributor may include a pipe which first directs theincoming flow away from the perforated baffle located immediately aheadof the coalescing section and then a half-pipe arranged to redirect theincoming flow toward the perforated baffle of the coalescing section.

A method of treating an oil-in-water stream includes the steps ofrouting the oil-in-water stream to a vessel as described above.

Objectives of this invention include providing a vessel which (1)performs coalescence and flotation in a single vessel; (2) handlesvolumes of at least 60,000 barrels per day; (3) accommodates a largevolume of water-to-be-treated at any given time relative to the overallinterior volume of the vessel; (4) reduces the footprint andconstruction costs of the water treating portion of a production system;and (5) allows existing vessels to be retrofitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-section front view of a preferred embodiment of atreatment vessel or cross-flow scrubber made according to thisinvention. The scrubber includes a coalescing section and flotationsection along with a specially designed inlet flow distributor, internalbaffle design, and outlet water collection pipe.

FIG. 1B is top view of the scrubber of FIG. 1A.

FIG. 2A is a cross-section view of a prior art vessel illustrating atypical radial eductor installation. This type of radial eductor is usedas a preferred embodiment of the gas-inducing device in the flotationsection of the cross-flow scrubber.

FIG. 2B is an illustration of the gas bubble distribution pattern of theradial eductor.

FIG. 2C is a cross-section view of the radial eductor of FIG. 2A.

FIG. 3 is a cross-section front view of the cross-flow scrubber of FIG.1 illustrating the distribution pattern of the inlet distributor to thecoalescing section of the scrubber.

FIG. 4 is a front view of a perforated baffle used in the scrubber ofFIG. 3.

FIG. 5A is cross-section front view of an alternate preferred embodimentof the cross flow scrubber having a solid baffle located between thecoalescing and flotation sections of the scrubber.

FIG. 5B is a top view of a scrubber having a solid baffle after thecoalescing section with the solid baffle arranged to provide dual flowthrough the flotation section.

FIG. 5C is a is a top view of a scrubber having a solid baffle after thecoalescing section with the solid baffle arranged to provide single flowthrough the flotation section.

FIG. 6 is an alternate preferred embodiment of the coalescing sectionwith one part of the coalescing section having a different sized packingor coalescing ball than the other.

FIG. 7 is a preferred embodiment of a solids removal device suitable foruse in the coalescing section of the scrubber.

FIG. 8A is an isometric view of a preferred embodiment of the differentsized coalescing balls.

FIG. 8B is an isometric view of a preferred embodiment of a coalescingring which may be used as an alternative to the coalescing balls.

ELEMENTS AND NUMBERING USED IN THE DRAWINGS

-   10 Vessel or cross-flow scrubber-   11 Inlet side-   13 Outlet side-   15 Top end-   17 Bottom end-   19 Inlet pipe-   21 Inlet flow distributor-   23 Longitudinally extending pipe with holes toward inlet side-   25 Shrouded (half) pipe facing holes of 23-   30 Coalescing section-   31 Perforated baffle-   33 Coalescing ball (packing)-   35 Coalescing ring (packing)-   37 First section-   39 Second section-   41 Solids removal device-   43 Solid baffle on outlet side of 30-   45 Inlet side of 30-   47 Outlet side of 30-   50 Flotation section-   51 Oil skimmer-   53 Radial eductor (gas-inducing device)-   55 Perforated baffle-   57 Cell-   61 Outlet water collecting pipe-   63 Treated water outlet pipe

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A water treating apparatus made according to this invention houses acoalescing section and a flotation section within a single vessel. Thevessel, or cross-flow scrubber, is more compact than prior artcorrugated plate interceptors (“CPIs”) and, because of its improvedperformance, can replace multiple CPIs. For example, a 12-foot diameterby 60-foot long (3.6576 m by 18.288 m) vessel can replace at least fourlarge CPIs and still achieve the same daily throughput as those fourCPIs.

Because the vessel can replace multiple CPIs, the number of inlet andoutlet valves and piping is reduced along with construction costs. Thecombination of a coalescing section and flotation section in one vesselalso improves overall performance when compared to vessels with only acoalescing section or a flotation section. This leads to a more costeffective solution for treating produced water to meet dischargerequirements.

In a preferred embodiment the vessel, which is elongated in thehorizontal longitudinal direction, houses an inlet flow distributorconnected to an inlet of the vessel and extending left and right of theinlet in the horizontal longitudinal direction of the vessel; acoalescing section located downstream of the inlet flow distributor in ahorizontal lateral direction between a perforated baffle and a secondbaffle and extending about a same length as the inlet distributor in thehorizontal longitudinal direction of the vessel; a gas flotation sectionlocated downstream of the second baffle in the horizontal lateraldirection of the vessel and extending about the same length as thecoalescing section in the horizontal longitudinal direction of thevessel; and an outlet water collecting pipe arranged to receive a flowexiting the gas flotation section, the outlet water collecting pipehaving one or more openings located along its length. The inlet flowdistributor is arranged to direct an inlet flow to the vessel in thehorizontal lateral direction across the vessel, the inlet flow withinthe vessel remaining a horizontal flow through the coalescing and gasflotation sections. A method of using the vessel includes the step offlowing the inlet oil-in-water stream horizontally through a vesselbetween the inlet flow distributor and the outlet water collecting pipe.

Referring first to FIGS. 1A & 1B, a longitudinal vessel 10 includes acoalescing section 30 located toward the inlet side 11 of the vessel 10and a flotation section 50 located toward the outlet side 13 of thevessel 10. The coalescing section 30 coalesces the incoming small oildroplets to larger oil droplets and helps the resulting larger oildroplets float to an oil skimmer 51 located toward the top end 15 of thevessel 10. The skimmer 51 is preferably arranged as a trough extendingin the longitudinal direction of the vessel 10. The flotation section 50makes use of radial eductors 53 (see e.g. FIGS. 1A-B & 2A-C), locatedtoward the bottom end 17 of the vessel, which generate small gas bubblesthat move vertically upward through the horizontal flow and attach tothe oil droplets and further float the remaining smaller oil droplets tothe oil skimmer 51.

The incoming oil-in-water stream enters in inlet pipe 19 and isdistributed to the coalescing section 30 by way of an inlet flowdistributor 21 having a longitudinal pipe 23 with holes on one side onlythat directs the incoming stream toward a shrouded (half) pipe 25 which,in turn, redirects the stream in an even flow to the coalescing section30 (see FIGS. 3, 5A, and 6). A HIFLO® spreader (Cameron Process Systems,Houston Tex.) or its equivalent is a suitable and preferred inlet flowdistributor 21.

Perforated baffles 31 (see e.g. FIG. 4) are located immediately ahead ofthe inlet side 45 and immediately after the outlet side 47 of thecoalescing section 30 to prevent fluid short circuiting and to improvevolumetric utilization of the vessel 10. Preferably, the cross-sectionalarea per each hole and number of holes in the baffles 31 are designed tohave a pressure drop in a range of 0.8 to 1.0 inch (2.032 to 2.54 cm)water column. The baffles 31, which span the length of vessel 10,distribute flow evenly or uniformly through the vessel 10. Theperforated baffle 31 on the outlet side 47 may have a solid baffle 43located after it which can be arranged for single or dual directionalflow through the flotation section 50 (see FIGS. 5A-C).

Referring now to FIGS. 1A, 6 and 8A & B, coalescing section 30 may usedifferent pre-selected sizes, shapes, and materials for the packing. Thepacking can be coalescing balls 33, coalescing rings 35, or other shapespreferable. The packing can be made of stainless steel or other suitablematerials for use in a high service temperature environment. If made ofstainless steel or its equivalent, the packing can be cleaned on anas-needed basis with 50 psi steam at 260° F. (344.7 kPa at 126.7° C.).

The packing can also be made of a polymer material which can sustainsteam temperatures (e.g., 260° F. or 126.7° C.). The polymer materialcan be TEFLON® (PFA), TEFZEL® (ETFE), HALLAR™ (ECTFE), KYNAR® (PVDF)material or their equivalent. If chemical cleaning methods are used, thepacking can be made of polypropylene having a service temperature of180° F. (82.2° C.). Steel-coated balls 33 or rings 35 can also be usedas packing.

Coalescing section 30 may have a same packing or mix of packingthroughout (see e.g. FIGS. 3 and 5A) but is preferably divided into afirst and a second section 37, 39, with the first section 37 having adifferent, pre-selected packing than the second section 39 such as, butnot limited to, a larger diameter coalescing ball or ring than thesecond section 39 (see e.g., FIGS. 1A, 6 and 8A & B). By way of example,first section 37 can use 2-inch (4.08 cm) size coalescing balls 33followed by second section 39 which uses 1-inch (2.54 cm) sizecoalescing balls 33. The reason for this arrangement is that the largerdiameter coalescing balls have higher open space to handle inlet fluidwith high solids concentration and prevent solid plugging, while thesmaller diameter coalescing balls provide higher surface coalescing areaper unit volume of balls to improve the coalescence of small oildroplets into larger droplets.

The use of different sizes, shapes, and materials for packing, as wellas dividing the coalescing section 30 into different sections 37, 39with different, pre-selected packing, provides options for vessel 10 tobe equipped or retrofitted to handle different treatment conditions suchas high solid concentration in the inlet stream or inlet streams havingdifferent physical properties such as but not limited to interfacialtension.

The solids which settle at the bottom end 17 the vessel 10 may need tobe removed on a regular basis. Removal can be done by way of a typicalsolids removal device 41 such as a HYDROTRANS™ solids fluidizationdevice (Cameron Process Systems, Houston, Tex.) (see e.g. FIG. 7) or itsequivalent, or by 50 psi (344.7 kPa) steam or other chemical cleaningmethods known in the art. The solids removal device 41 preferablycreates a rotary, vertiginous, or cyclonic flow external to the device(i.e., straight in and rotary or cyclonic out) and fluidizes the solidsfor removal by a slurry line.

Referring now to FIG. 5A, a solid baffle 43 can be used after thecoalescing section 30 to divert the fluid exiting the section 30longitudinally from one end 11 of the vessel 10 to the other end 13 ofthe vessel 10. The solid baffle 43 can be arranged to provide dual flow(see FIG. 5B) or single flow through the flotation section 50 (see FIG.5C).

Multiple perforated baffles 55 installed in the flotation section 50divides the flotation section 50 into multiple cells 57 and helpdistribute flow uniformly across or through flotation section 50.Preferably, the cross-sectional area per each hole and number of holesin the baffles 31 are designed to have a pressure drop in a range of 0.8to 1.0 inch (2.032 to 2.54 cm) water column. Gas-inducing devices,preferably one or more radial eductors 53 or their equivalent, can beinstalled inside each cell 57.

Treated water exits vessel 10 by first entering an outlet watercollecting pipe 61 which extends in the longitudinal direction of vessel10 and has one or more openings along its length, preferably aperforated pipe or a pipe with a slot. The pipe 61 reduces shortcircuiting of the outlet fluid and prevents oil droplets being draggedinto the water outlet stream exiting the treated water outlet pipe 63.

The outlet water collection pipe 61, in combination with the inlet flowdistributor 21 and the multiple perforated baffles 31, 55 work to doublethe volumetric utilization of vessel 10—that is, the total volume of theoil-in-water being treated in the vessel relative to the total volume ofthe vessel—to greater than 90% from less than 45%. For example, thetotal volume of a 12-foot diameter by 60-foot long (3.6576 m by 18.288m) vessel 10 is approximately 50,760 gallons (about 192,147 liters). Autilization of 90% allows the filled volume to be approximately 45,684gallons (about 172,933 liters). Because of this increased utilization,the length of vessel 10 can be reduced by about 50% compared to priorart vessels and trains yet treat an equal volume of throughput as thoseprior art vessels and trains. Therefore, vessel 10 is more compact andits construction costs are reduced relative to prior art vessels andtrains.

A method of treating an oil-in-water stream includes the step of routingan oil-in-water stream to vessel 10 as described above. The flow ratethrough vessel 10 can be in the range of 1 ft/min to 10 ft/min (0.3048m/min to 3.048 m/min), and more preferably in the range of 2 ft/min to 5ft/min (0.6096 m/min to 1.524 m/min). The optimal flow rate designdepends upon the inlet fluid properties, inlet oil droplet size, and theoutlet oil-in-water specification.

While preferred embodiments of vessel 10 have been described, thepreferred embodiments may not be all possible embodiments of theinvention. The scope of the invention is defined by the followingclaims, including each claim's full range of equivalency.

1-26. (canceled)
 27. A method of treating an oil-in-water streamcomprising providing a vessel for treating the oil-in-water stream, thevessel elongated in a horizontal longitudinal direction and having aninlet at one end thereof and an inlet flow distributor disposed thereinand extending left and right of the inlet of the vessel; flowing thestream in a horizontal lateral direction from the inlet, through theinlet flow distributor and into a coalescing section within the vessel;flowing the stream in the horizontal lateral direction from thecoalescing section to a flotation section within the vessel, andtreating the stream in at least one of the coalescing section and theflotation section by floating oil from the stream to an oil skimmerwithin the vessel.
 28. The method according to claim 27 furthercomprising directing treated water from the flotation section to anoutlet water collecting pipe.
 29. The method according to claim 27wherein the coalescing section comprises at least a perforated baffle.30. The method according to claim 29 wherein the gas flotation sectionextends about the same length as the inlet flow distributor is upstreamof a second baffle.
 31. The method according to claim 27 wherein thecoalescing section includes a packing and is divided into a first and asecond section, a packing of the first section being a differentpre-selected packing than a packing of the second section.
 32. Themethod according to claim 31 wherein the packing of the first and secondsections differ in size or material or size and material.
 33. The methodaccording to claim 27 wherein the flotation section is divided by one ormore perforated baffles.
 34. The method according to claim 28 whereinthe outlet water collecting pipe comprises one or more openings locatedalong its length.
 35. A method of treating an oil-in-water stream in avessel comprising directing the oil-in-water stream to an inlet flowdistributor connected to an inlet of the vessel, the inlet flowdistributor extending left and right of the inlet and arranged to directan inlet flow to the vessel in a horizontal lateral direction across thevessel; directing the stream to a coalescing section located downstreamof the inlet flow distributor and between a perforated baffle and asecond baffle, the coalescing section extending about a same length asthe inlet flow distributor and configured so the inlet flow within thevessel remains a horizontal lateral flow through the coalescing section;and directing the stream to a gas flotation section located downstreamof the second baffle
 36. The method according to claim 35 furthercomprising directing treated water from the flotation section to anoutlet water collecting pipe.
 37. The method according to claim 36wherein the outlet water collecting pipe comprises one or more openingslocated along its length.
 38. The method according to claim 35 furthercomprising treating the stream in at least one of the coalescing sectionand the gas flotation section by floating oil from the stream to an oilskimmer within the vessel.